In asymmetric digital subscriber line (ADSL) and very high speed digital subscriber line (VDSL) environments, a retransmission (ReTx) technique may be utilized for ensuring quality of transmission for latency-insensitive data, such as video.
The retransmission scheme used in xDSL systems supports (with small variations) both asynchronous transfer mode (ATM) and packet transfer mode (PTM) protocols and has been designed such that elementary frames that can be retransmitted are formed in the physical layer (PHY). It is also proposed that for ADSL, retransmission is only used for the downlink, whereas for VDSL, retransmission can be used either for the downlink only or for both uplink and downlink.
A transmitter supporting the retransmission scheme implements a retransmission queue for storage of elementary frames in order to have access to previously sent elementary frames in the event that a request for retransmission is received. A receiver supporting retransmission scheme implements a rescheduling queue that resequences elementary frames in the event that elementary frames are received out of order due to retransmission.
Management of the retransmission queue (at the transmitter) and the rescheduling queue (at the receiver) can be done in various layers of the xDSL PHY, including the transport protocol specific transmission convergence (TPS-TC) layer and the physical media specific transmission convergence (PMS-TC) layer. However, existing retransmission techniques proposed so far assume that both retransmission queue and rescheduling queue are implemented in the same layer.